Table of Standards (ASTM MANHOLES)

8/10/2019 Table of Standards (ASTM MANHOLES)

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TABLE OF STANDARDS

ASTM: DESIGN AND CONSTRUCTION OF SANITARY AND STORM SEWERS

STANDARDS FOR THE DESIGN OF MANHOLES

DESCRIPTION STANDARD

GENERAL SHAPE & DIMENSION Inside diameter must be least 4ft

Maintain the 4ft diameter up to a conical

section

Frames under diameter at least 24inches P to

30 inches, within 2ft of the surface.

Walking space of manhole 3ft x 4ft vault

STEPS Manhole steps should be wide enough for a

man to place both feet on one step, and should

be designed to prevent lateral slippage off the

step.

General spacing of steps, 12 to 16in intervals(30-50cm)

CHANNEL AND BENCH For sizes of 15 inches and larger, the required

channel height rarely is less than three- fourths

of the diameter.

The bench should provide good footing for a

workman and a place where minor tools and

equipment can be laid.


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STANDARDS FOR HE DESIGN OF MANHOLES

0.5in /ft is specified in some areas to provide

safer footing.

MAN HOLES ON LARGE SEWERS Where a sewer is larger than 2ft and the small

sewer type of man hole is used, the diameter of

the manhole should be increased sufficiently to

maintain an adequate width of bench,

preferably a foot or more on each side.

For sewers up to 3ft in diameter, covers

sometimes are used having a clear opening of

3ft to accommodate cleaning equipment

equalling the sewer diameter.

Many authorities do not use openings larger

than 2ft, openings larger than 3ft are used onlyin special cases.

SHALLOW MAN HOLES If the depth of the invert is only 2 or 3ft, all

maintenance operations can be conducted

from the surface. A manhole 2 or 3ft in

diameter at the bottom generally suffices in

these cases; narrow slots also have been used.

If man hole is usual type, height from the bench

to surface is in the range 2 to 4ft or 5ft( 0.6 to

1.2 or 1.5m), with the shaft tapering to a 22inchclear opening , the structure is one in which a

man cannot work effectively.

Brick or concrete block walls normally are built

8 inches (20.3cm ) thick at the shallower

depths, and may increase to 12 inches (0.3m)

below 8 to 12ft (2.4 to 3.6m) from the surface


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The outside walls of brick or block manholes

should be filled completely with cement

mortar. The outside walls of brick or block man

holes should be parged with cement mortar not

less than 1/2in (1.3cm) thick. In wet areas it is

advisable to apply a coating of bituminous

damp-proofing compound.

BENDS A curve of very short radius causes energy

wasting turbulence. Some authorities

recommend for optimum performance that the

radius of the centre line be three times the pipe

diameter or channel width. Reasonably

satisfactory conditions usually can be obtained

if the radius is not less than 1.5 times the

diameter.

Bands of less than 90 degrees can of course be

accommodated more easily. For angles

substantially less than 90 degrees on sewers

larger than 12 inches in diameter, the manhole

maybe centre d over the pipe

DROP MANHOLES Drop manholes should be used sparingly and

generally, only when it is not economically

feasible to steepen the incoming sewer. Some

engineers eliminate drops by using verticalcurves.

BUILDING SEWERS Building sewers also called house connections,

service connection, or source laterals, are the

branches between the street sewer and the

property or curb, serving individual properties,

and usually are required to be 4, 5 or 6 inches

in diameter (10 to 15inches) preferably with a

slope of 1/4 in/ft (2cm/m) or 2 percent.


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GUTTER INLETS A horizontal opening in the gutter covered by

one or more grates through which the gutter

flow passes is called a gutter inlet. Tests

indicate that grates with slots parallel to the

curb are the least subject to plugging and

provide the best inflow conditions.

Width of the opening must not be greater than

1inch (2.5cm) so that bicycle tyres will not pass

through.


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WATER AND SEWERAGE AUTHORITY (WASA) OF TRINIDAD AND TOBAGO

WATER AND WASTE WATER DESIGN GUIDE MANUAL

DESIGN STANDARDS

DESCRIPTION STANDARD

Co efficient of roughness For all pipe materials, the coefficient of roughness should be set as 0.013

Minimum Pipe Size For residential areas, the minimum pipe shall be 200 mm diameter

For commercial and industrial areas, the minimum pipe size shall be 250

mm diameter.

Flow Velocities The maximum velocity shall not be greater than 3.0 m/sec with the pipe

flowing full and the

minimum velocity shall not be less than 0.60 m/sec with actual flow on a

daily basis. The depth of flow should never exceed 75% of the internal

diameter of the sewer.

System Layout Location of Wastewater

Main

All new wastewater mains shall be located within the road allowance

Location of replacement wastewater mains shall be determined

specifically based on the location of existing utilities and other site

conditions and will be dealt with as situation arises. Preferably, sewers areto be 1.5 m offset from roadway centreline. System arrangement shall

include redundancy and overflows to propose alternate routes in case of

blockage. Overflow shall be

rerouted in the sewer system. Sewer easements are required if sewer

located out of roadway

Gas pipelines need a minimum separation of 0.9 m at crossings. See

section 5.5.3 for distances


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from drinking water lines & pipes

Forcemains Pipe Size Forcemains shall be sized to have a flow velocity in the range of 0.7 to 3.0

m/s, with the lower limit being preferred for the initial phase. The

minimum size of the forcemain shall be 100 mm in diameter

Pipe Depth Consultants shall allow a minimum of 1.2 m of cover for forcemains

Maintenance Chamber (Manhole)1.

At maintenance chambers where pipe sizes change from smaller pipe size to a larger downstream pipe size, match the pipes obvert

elevations. It is not permissible to design downstream pipe size smaller than the upstream pipe size.

2.

Drop maintenance chambers shall be provided where the difference in elevation is greater than 0.60 metres. The drop pipe shall be

one size smaller than the wastewater main. The economic feasibility of providing deeper wastewater mains versus excessive invertdrops drop maintenance chambers, or excessively steep benching shall be ascertained prior to finalizing the design. Prefabricated

drops internal to the maintenance chamber are not permitted on 1200 mm diameter maintenance chambers. Where the

maintenance chamber depth exceeds 10 m, provide safety grating.

3.

Watertight and locking covers shall be provided on maintenance chambers located on all easements and in areas where

maintenance chambers are susceptible to flooding. Where significant sections of wastewater mains are provided with watertight

covers, extended vents may be required which shall be determined by the Consultants on a case-by-case basis. Frames and covers

to be a floating style (NF80 or 90) capable of withstanding H-20 loading.

4.

Tee maintenance chambers may be used for wastewater mains 1200 mm or larger in diameter

5.

Sanitary sewer service connection to a maintenance chamber should be avoided. However, it may be permissible should the

proposed sanitary sewer service falls within the same obvert elevation of the sanitary sewer entering the maintenance chamber.

6.

For commercial and industrial establishments, an inspection maintenance chamber must be placed at a location immediately

behind the property line to service the lateral connection.

7.

All enclosures and rails should be corrosion resistant.


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MANHOLE HYDRAULICS

Alignment Change Required Drop

15o45o min. 0.030 m

45o90o min. 0.050 m

*Pipe Slopes & Manhole distances

The minimum slopes shown are those required for self-cleansing velocity set as 0.7 meter per second, The maximum length between manholes and

the absolute minimum slopes for different sewer sizes shall conform the following:

SEWER SIZE (mm) MAXIMUM LENGTH (m) BETWEEN

MANHOLES

MINIMUM SLOPE (m/100m)

200 90 0.40

250 110 0.28

300 110 0.20

350 110 0.17

375 110 0.15

400 120 0.14

450 120 0.12

525 120 0.10

600 150 0.08

900 150 0.046

1200 Assess 0.031

1800 Assess 0.020


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*Street Line Connection

Single family and semi-detached dwellings in residential areas shall have a minimum of 150 mm diameter street line connection.

Dual connections or two separate lines in a common trench are acceptable in residential areas where the difference in basement elevation does not

exceed 0.60 m. Two or more units serviced on a common line with wye branches are acceptable. Where the diameter of the lateral connection isgreater than or equal to half the diameter of the wastewater main, the connection shall be made with a tee-wye or wye connection. The minimum and

maximum cover at property line shall be 1.2 m and 1.8 m, respectively. A 2% minimum grade for lateral connections shall be maintained. Pipe size

change must be made through similar quality eccentric pipe reducers. In multiple family blocks in residential areas, the lateral connections shall meet

the following requirements:

Connection Size and Grade

Diameter of Drain (mm) Slope Of Drain

2% 4%

Maximum Number of Fixture Units per Connection

150 840 1000

200 1920 2300

250 3500 4200

300 5600 6700

375 10000 12000

Table of Standards (ASTM MANHOLES)

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